You can call it hogwash and call BS all you want. It doesn't change the facts (particularly, look up singularity and jnode.)
No amount of waxing eloquent or hogwash is ever going to change the fact that this is simply not possible in ANY mid to high level language much less Java. You use the right tool for the job or you don't get the job done. You could have Java as the GUI but you most certainly would not be able to use Java as is to get any type of OS code to do anything close to managing the entire system.